The field of medical radiography has undergone profound changes in the past few years. In particular, the development of new types of recording media using photoluminescent memory plates, well known by the name of "phosphor plates", has enabled digital medical imaging to be developed. Traditionally, radiographic images were obtained on photosensitive plates which, after processing in photographic processing baths, enable the radiographic image to be displayed. Technological developments in the past few years with regard to image processing have made it possible to envisage obtaining radiographic images which can be exploited from digital data.
A digital medical imaging unit is associated with a radiography system using "phosphor cartridges", that is to say cartridges provided with photoluminescent memory plates used to form a latent analog radiographic image.
In order to be able to exploit the latent image contained in the photoluminescent memory plate, the cartridge is inserted into a reading device in which the plate is extracted form the cartridge and then scanned with a reading beam so as to excite the plate locally. This excitation causes a light emission which is a function of the irradiation previously received by the plate. By means of a photosensitive sensor, the reading device converts the intensity of the radiation emitted by the plate into an analog electrical signal which is then converted into digital data. By scanning the plate, the reading device therefore supplies, for each plate, a digital representation of the information carried by the photoluminescent memory plate. The reading device is very often associated with an automatic cartridge dispenser enabling a plurality of cartridges to be disposed at the entry to the reading device. After the processing of a cartridge by the reading device, the latter erases any residual information on the plate and returns the cartridge to the dispenser and takes therefrom a new cartridge in order to process it.
The digital representation coming from the reading device is then processed by a suitable digital processing unit provided with distinct processing algorithms dependent on the type of radiographic image recorded on the photoluminescent memory plate. To do this, information relating to the type of radiographic examination carried out with the cartridge concerned is supplied to the processing unit.
The medical imaging unit also comprises a workstation which, after receipt of the digital medical images, makes it possible to edit the various images contained in the memory of the processing unit.
A description will now be given of the conventional use of a digital medical imaging unit. When it is desired to carry out a radiographic examination of a patient by means of a digital medical imaging unit, the information required for the identification of the patient is first of all introduced into the computer. In general the surname of the patient and his first name are introduced, sometimes his sex and his age. A unique identification number, which can be coded and printed in the form of a bar code on labels, is made to correspond to this information. Normally, each phosphor cartridge is identified unequivocally in order to be able to be recognized by the processing unit. In one particularly advantageous embodiment, the cartridges are identified by means of a bar code. During the radiographic examinations the type of examination recorded in each cartridge is introduced into the processing unit so as to obtain processed digital images whose visual presentation is close to the presentation obtained with silver halide radiographic plates. It is obvious that, when other universal types of processing are available, it will be possible optionally to dispense with such processing. Advantageously, in some medical imaging units, this information can be introduced into the processing unit by means of a bar code reader, preferably portable, which will capture the information directly at the time of the radiographic examination. In this way any possible mixing up of the cartridges is avoided when the examination requires more than one cartridge for the patient.